1. Field of the Invention
The present invention relates generally to integrated circuit (IC) fabrication, and more particularly but not exclusively to deposition of IC fabrication materials using a print head.
2. Description of the Background Art
The use of ink jet technology to print on paper is well known. A typical ink jet print head has several nozzles that are coupled to an ink reservoir. Ink from the reservoir are dispensed through the nozzles to form a pattern on paper. The ink jet print head may be scanned relative to the paper, or vice versa, to cover a large area.
FIG. 1 schematically illustrates the operation of an exemplary ink jet print head 20. Print head 20 may be of the type available from Ink Jet Technology Inc. of San Jose, Calif., for example. Print head 20 may have any number of nozzles 22 (i.e., 22-1, 22-2, . . . ) but only four are shown for clarity of illustration. A digital firing pattern may be serially loaded into a firing register 23 of print head 20 to enable or disable a nozzle 22. Each nozzle 22 may have a corresponding bit position in firing register 23. A logical “1” enables a nozzle 22 to fire (i.e., dispense ink), while a logical “0” disables a nozzle 22 from firing. For example, assuming a 4-bit firing register 23, a firing pattern of “1000” may be loaded into firing register 23 to enable firing of nozzle 22-1 but not nozzles 22-2, 22-3, and 22-4; a firing pattern of “1001” may be loaded into firing register 23 to enable firing of nozzles 22-1 and 22-4 but not nozzles 22-2 and 22-3; and so on.
Each nozzle 22 may be coupled to an ink reservoir via a chamber (not shown). Ink flows from the reservoir into the chambers prior to being dispensed out of nozzles 22. The amount of ink drawn into the chambers, and thus the amount of ink dispensed by nozzles 22, may be controlled by loading an appropriate timing pattern into a timing circuit 24. Timing circuit 24 converts the timing pattern into timing pulses that are applied to all nozzles 22.
The use of ink jet technology in the fabrication of integrated circuits (IC's) is disclosed in commonly-assigned U.S. Pat. No. 6,436,843, which is incorporated herein by reference in its entirety. Unlike paper printing applications where the emphasis is on printing sharply delineated marks, film deposition in an IC fabrication process is concerned with dispensing a uniform amount of material on a substrate. This uniform amount may be in terms of unit volume per unit area. Because of manufacturing tolerances, the nozzles of a print head may dispense varying amounts of material for the same timing pulses. The amount of material dispensed from nozzles, which may be in terms of drop volume, may vary by 10% or more from nozzle to nozzle for a given print head.
One way of compensating for variations in drop volume is to provide a separate timing circuit for each nozzle. This approach, however, requires relatively expensive electronics and bulky cabling as each nozzle may have to be connected to its own drive circuit with independent timing. Using a relatively low-cost, off-the-shelf print head poses its share of problems because such a print head typically employs a serially loaded firing register and a common timing circuit for all nozzles. Conventionally, a common timing circuit does not allow for the use of a tuned timing pattern for each individual nozzle without adversely affecting print frequency.